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When it comes to fighting climate change, most people think about shrinking their carbon footprints by reducing the amount of the heat-trapping gas, or carbon dioxide, generated when they flip on a light switch, drive a car, or put on the air conditioner.

But scientists and policy makers have long been intrigued by a larger-scale approach: the idea of removing carbon dioxide - separating out the greenhouse gas from the exhaust coming out of the flues of coal plants or other sources, and keeping it out of the atmosphere. The Department of Energy has sunk millions of dollars into more than a dozen projects aimed at the problem, through a program that funds risky but potentially transformative research.

But earlier this month, an ambitious project to build a system that could capture 90 percent of the carbon dioxide from a coal-fueled plant in West Virginia was put on hold by one of the largest electric utilities in the United States because of the uncertain state of climate policy and the weak economy.

The announcement that American Electric Power was halting the initiative, which had been supported by the federal government, was a serious blow to this particular effort to fight global warming. But it was only one of a slew of efforts being devised with that approach, which are still moving forward.

At start-up companies and in research laboratories, scientists are devising materials and technologies that could help remove or store carbon dioxide. The approaches span the gamut from basic science research in the laboratory to a company that is using carbon dioxide as a raw material to manufacture everyday plastics or chemicals - a technology that could enable the making of greenhouse-gas-based house paint or plastic bottles.

“If we’re really going to address this problem realistically, we have to have a variety of opportunities,’’ said T. Alan Hatton, a chemical engineering professor at the Massachusetts Institute of Technology.

For Hatton, the problem of separating and capturing carbon dioxide is, in some ways, a return to themes from earlier in his life.

Hatton grew up in South Africa, where his father commissioned and ran large power plants, and as a young scientist he wrote his master’s thesis about a method for absorbing carbon dioxide. His interest at the time was an industrial, not an environmental application.

But over the past three years, Hatton and research engineer Fritz Simeon have been working on creating a laboratory-scale demonstration that uses an electrochemical technique to selectively remove carbon dioxide from the exhaust of coal plants. The work depends on a chemical compound called a quinone, which was first demonstrated to react with carbon dioxide electrochemically by Mark Wrighton, a former provost at MIT, more than two decades ago.

The team has gotten support from Siemens, a German industrial giant, and from the federal Advanced Research Projects Agency-Energy and plans to have a demonstration project by next year.

One of the goals is to make the process less expensive and energy-intensive than current methods.

Using a completely different tactic, a start-up company called Novomer Inc., with corporate offices in Waltham, is working on finding a way to make carbon dioxide an ingredient in everyday plastics and coatings found on metals and wood.

The company uses a technology developed by a Cornell University professor. A catalyst, a chemical compound that triggers a reaction, causes carbon dioxide or carbon monoxide and another substance to form a plastic or different chemical.

Such materials are everywhere, making possible many consumer products, ranging from Spandex to house paint, as well as everyday plastics.

“Everything we do has about 50 percent carbon dioxide or carbon monoxide in it,’’ said Jim Mahoney, the chief executive of Novomer.

The company received a $20.5 million grant from the Department of Energy last year and has raised $20 million from private investors.

Being “green’’ is an important component of any new technology, but as important are costs and whether it is better than what’s already on the market.

“When we talk to customers, environmental aspects are very important,’’ Mahoney said. “But it has to come in at a competitive price and cost.’’